My roommate bought a Vive and there was something similar to this in the free Aperture Labs demo, but it was a computer model. To actually see it in action is mind-blowing (I assume this is a scan of a real person)

Was just wondering that. I recently worked on getting a phone's position from its accelerometer and gyroscope, and the position kept changing even though the device is still due to the integration drift... So I was really surprised when I saw the gif.

Any sensor is going to have small errors, especially a digital one that only records at discrete intervals (2 times per second, 1000 times per second, etc.). Those little errors compound very quickly into big problems when you integrate to try to deduce speed and again to get position.